1. Field of the Invention
The present invention relates to an ink set preferably used for ink jet recording.
2. Background Art
In ink jet recording, ink droplets are generated and ejected by static electricity-driven ejection, air pressure-driven ejection, piezoelectric device deformation-driven ejection, thermal bubble formation-driven ejection or the like and deposited onto recording paper. The water-base ink used in this method is prepared by dissolving or dispersing various dyes in water or an organic solvent.
In recent years, waterfastness on plain paper is required of the ink jet recording. In order to obtain a water-base ink that can yield an image having good waterfastness, various studies have been made on the addition of polyamines, including polyethyleneimine and modified polyethyleneimines, in combination with dyes to the ink.
For example, Japanese Patent Laid-Open No. 119280/1987 and Japanese Patent Publication No. 91495/1995 disclose, as a waterfast composition for ink jet recording, an ink containing a hydroxyethylated or hydroxypropylated polyethyleneimine and a dye component. As far as the present inventors know, however, the hydrophilicity of the polymer is so large that satisfactory waterfastness cannot be attained depending on degree of hydroxyethylation or hydroxypropylation of the polymer. This is because in the polymer of these documents about 50 to 95% by mole of the side chain is accounted for by a hydroxyethyl group or a hydroxypropyl group.
Japanese Patent Laid-Open Nos. 255876/1990, 26876/1990, and 188174/1991 disclose, as a waterfast water-base ink composition, a composition containing a polyamine, with a primary amino group, having a molecular weight of not less than 300, an anionic dye, a stability imparting agent, and a wetting agent.
Japanese Patent Laid-Open No. 305011/1995 discloses a method for imparting waterfastness to a water-base ink containing: a basic water-soluble polymer; an anion dye using a volatile base as a counter ion; and a buffer using a volatile base as a counter ion, wherein the dissociation constant of each base is regulated. In the water-base ink, when the ink is in the state of an ink liquid, the dissociation of a cationic polymer is suppressed. On the other hand, on paper, the volatile base is evaporated to allow a salt-forming reaction between the polymer and the dye to proceed, thereby imparting the waterfastness to the ink.
Japanese Patent Laid-Open No. 113743/1996 discloses, as a waterfast ink, a water-base ink containing an anion dye having an azo group, and an amino acid type polyamine or polyethyleneimine.
Further, Japanese Patent Laid-Open Nos. 167374/1989, 80470/1990, and 292275/1995 and Japanese Patent Publication Nos. 30268/1995 and 68462/1995 disclose an ink having improved waterfastness attained by using a polyamine dye prepared by combining a polyamine, such as polyethyleneimine, polyvinylamine, or polyallylamine, with an azo dye having a reactive functional group.
As far as the present inventors know, the above conventional inks can ensure given waterfastness, but on the other hand, the lightfastness is poor. In particular, in a full-color image formed using a plurality of inks, the presence of only one color having poor lightfastness results in a change in hue, which leads to extremely deteriorated quality of the color image. Thus, a higher level of lightfastness is required of the inks for a full-color image. For example, in the ink disclosed in Japanese Patent Laid-Open No. 113743/1996, utilization of a dye having a specific structure is indispensable. For this reason, the range of dyes which can be selected is so narrow that it is difficult to prepare inks having desired properties (for example, hue and density). In the inks for realizing a full-color image, it would be desirable that a wide variety of colorants could be used.